Alginate ropes, method of preparation and use

ABSTRACT

A process for preparing an alginate rope, which process comprises the steps of: (a) extruding an aqueous solution of a water soluble alginate into a coagulation bath; (b) contacting the extruded water soluble alginate with a source of a cation capable of forming a water insoluble alginate salt so as to produce a tow of water insoluble alginate fibers; (c) twisting the water insoluble alginate fibers of the tow; and (d) stretching the fibers up to 250% of their original length. The alginate rope prepared according to the process of the invention may be used as a surgical pack material or in the treatment of cavity wounds.

The present invention relates to a process for the preparation of analginate rope, an alginate rope prepared according to that process, adressing comprising the alginate rope and methods of use thereof.

Alginate fibres have been known for some time as being useful in thepreparation of surgical dressings. For example, United Kingdom PatentNo. 653341, published in 1951, describes surgical dressings formed fromfibres of calcium alginate. The employ of alginate fibres is oftendesirable over other conventional materials employed in surgicaldressings, such as cotton and the like, in view of the superiorbiocompatibility properties of alginates.

Calcium alginate fibres have subsequently been modified to improve theirrelative insolubility in water or wound exudate matter. Bonniksen inGB-A-653341 therefore proposed that a proportion of the insolubilisingcalcium ions in calcium alginate be replaced by solubilising sodiumcations. The resulting process has become known as "conversion" ofcalcium alginate to form a mixed salt alginate. Such mixed saltalginates exhibit a further advantage associated in the employ ofalginates in wound treatment, in that such mixed salt alginates havingimproved solubility in water or wound exudate matter form a protectiveand useful gel like structure that results over time, and is beneficialto the wound healing process.

Skilled artisans are therefore well aware that it is often desirable toemploy alginates in wound dressings and various types of dressing formedfrom fabrics comprising alginate fibres are therefore known, includingnon-woven alginate rope. Alginate rope is particularly useful forsurgical packing and the management of cavity wounds.

Alginate rope is conventionally prepared via a multistage processinvolving extruding an aqueous solution of sodium alginate into acalcium ion source, stretching the resulting calcium alginate fibres tobetween 160 and 250% of their original length, optionally converting aproportion of the calcium ions to sodium ions, then crimping, cutting tostaple length, carding and textilling the tow.

Such multistage processes are time consuming and expensive, inter alia,involving the use of multiple spinnerets. Furthermore, alginate ropesproduced by conventional techniques as described above generally lackstructural integrity which often results in unravelling thereof duringuse or disintegration on removal from a wound site, whereby residualalginate fibre can be left in the wound site. The residual fibres aregenerally picked out in tiny pieces, or removed by irrigation, from thewound site. Such removal requires considerable skill, and there istherefore a need for an alginate rope which can be lifted from a woundin one piece. An example of a currently employed alginate rope isavailable under the trade mark SORBSAN, this SORBSAN rope being a thinsliver which often lacks structural strength and use thereof cantherefore be disadvantageous for the reasons described above.

In view of the above lack of structural integrity associated withcommercially available alginate rope products, other materials, such ascotton gauze and the like, are often employed in situations where itmight have been desirable to employ alginate rope products, such as inthe treatment of sinus cavities and the like. Such alternativematerials, cotton gauze being a typical example, lack the abovedescribedadvantageous biocompatibility or gel-forming properties associated withalginates.

We have now discovered a process of preparation, and a resultingalginate rope product, which alleviate the above problems. Inparticular, we have discovered a process of preparing an alginate ropewhich is essentially a single stage process and eliminates the necessityto employ the above described steps of crimping, cutting, carding andtextilling the tow. Furthermore, an alginate rope product is provided bythe present invention which exhibits greatly improved structuralintegrity, this being advantageous, inter alia, in handling the dressingbefore application to a wound site and in many cases makes removal froma deep wound site much easier.

There is therefore provided by the present invention a process ofpreparing alginate rope, which process comprises the steps of:

(a) extruding an aqueous solution of a water soluble alginate into acoagulation bath;

(b) contacting the extruded water soluble alginate with a source of acation capable of forming a water insoluble alginate salt so as toproduce a tow of water insoluble alginate fibres;

(c) twisting the water insoluble alginate fibres of the tow; and

(d) stretching the fibres up to 250% of their original length.

Water soluble alginates include, for example, sodium alginate, potassiumalginate, lithium alginate, ammonium alginate and magnesium alginate.Preferably the water soluble alginate used in the process of the presentinvention is sodium alginate. Suitably the aqueous solution of the watersoluble alginate is extruded into a coagulation bath containing a sourceof a cation capable of forming a water insoluble alginate salt.

Cations capable of forming water insoluble alginate salts include, forexample, calcium and zinc cations. Preferably the cation capable offorming a water insoluble alginate used in the process of the presentinvention is calcium ion.

Suitably the source of the insolubilising cation comprises a saltthereof, such as chlorides, sulphates, nitrates, gluconnates and thelike. Aptly a chloride salt of the insolubilising cation is employed.

It may be preferred to prepare a mixed salt alginate rope productwhereby at least some of the insolubilising cations of the alginatefibres produced by step (b) are replaced by cations capable of forming awater soluble alginate salt. Optionally, a process according to thepresent invention comprises, following step (d), treating the waterinsoluble alginate fibres with a source of a cation capable of forming awater soluble alginate salt so as to replace at least some of theinsolubilising cations present in the alginate fibres with cationscapable of forming a water soluble alginate salt.

Suitably, preparation of a mixed salt alginate may be achieved bytreating sequentially with an acid and a source of a cation capable offorming a water soluble alginate. Generally an acid bath is used in theconversion procedure for treatment with a suitable acid and asolubilising cation. Desirably the pH should be carefully controlledduring the conversion procedure in order to avoid removal of more thanthe desired percentage of calcium cations, suitably at least 10% of theinsolubilising cations are removed. In a particularly preferredembodiment no more than about 20% of the insolubilising cations areremoved. Typically, during acid treatment, the pH of the bath should bein the range of 1 to 3, aptly about 1.5 to 2.5. Control of pH can beachieved by standard techniques, such as titration of the acid bath andthe like.

Suitably organic or inorganic acids can be used in the treatment of thewater insoluble alginate fibres. Aptly mineral acids such ashydrochloric, sulphuric and nitric acids may be employed, hydrochloricgenerally being preferred.

The retention time, which is to say the time for which the insolublealginate is in contact with the acidic medium, may be any suitableperiod of time, for example from 1 second to 5 minutes. Retention timesin the order of from 5 to 60 seconds such as about 20 or 30 seconds arequite suitable. It will be appreciated that the degree of conversion maybe controlled by a combination of the pH of the acid bath and theretention time.

Suitable basic sources of a cation capable of forming a water solublealginate include, for example, salts such as carbonates, hydroxides andthe like, of solubilising cations such as sodium, potassium, lithium,ammonium and magnesium as hereinbefore described.

In a preferred embodiment, the present invention provides a process forthe preparation of an alginate rope comprising 30:70 Ca:Na to 90:10Ca:Na mixed salt alginate fibres, suitably 40:60 Ca:Na to 90:10 Ca:Na,more suitably 60:40 Ca:Na to 85:15 Ca:Na and even more suitably 70:30Ca:Na to 85:15 Ca:Na. In a particularly preferred embodiment the presentinvention provides a process for the preparation of alginate ropecomprising about 80:20 Ca:Na mixed salt alginate fibres.

Aptly the fibres are extruded at a linear speed in the range of 1meter/minute to 40 meters/minute, more aptly at a speed in the range of3 meters/minute to 20 meters/minute, even more aptly at a speed in therange of 4 meters/minute to 10 meters/minute, and preferably at about 5meters/minute.

Suitably, twisting of the water insoluble alginate fibres is achieved byextruding the fibres from a spinneret which is rotated at a speed in therange of 3 to 800 rpm, more suitably at a speed of 3 to 400 rpm, mostsuitably at a speed of 3 to 100 rpm, and preferably 3 to 50 rpm.

The number of holes and hole size of the spinneret employed in thepresent invention varies depending on the nature of the required endproduct. Generally, spinnerets having a hole size of 20 to 200 micronsin diameter are employed, suitably 40 to 120 microns and more suitably60 to 80 microns. Aptly a spinneret having 100 to 400 holes may beemployed in the preparation of thin sliver alginate rope product,typically of thickness 0.8 to 1.2 mm, which can be subsequently employedin the production of a yarn suitable to be textilled to provide surgicalswabs, dressing fabrics and the like. Alternatively, a 5,000 to 10,000hole spinneret can be used to prepare a relatively thicker alginate ropeproduct, suitably of 2 to 4 mm, for example of 2.8 to 3.2 mm inthickness, which is itself suitable for use in sinus cavities and thelike without further significant processing. (It will be appreciatedthat although these are termed ropes, they often appear ribbon-like).

In addition to the above variation in the number of holes and hole size,it may be desirable to vary the hole pattern provided on the spinneret.For example, the holes may be substantially evenly distributed over thespinneret face, alternatively a denser population of holes may beprovided in a localised region of the spinneret face. The spinneret maybe of variable cross sectional shape, such as circular, rectangular andthe like.

It is generally preferred that step (d) comprises stretching the waterinsoluble alginate fibres in the range of 120 to 200%, suitably 140 to180% of their original length, and more suitably the fibres arestretched to 150 to 170% of their original length.

Suitably a process according to the present invention further compriseswashing the alginate rope, generally with deionised water, and aptly mayalso include a drying step. Suitably the drying involves treatment ofthe rope with a volatile drying agent and/or drying in air suitably byemploying a stream of hot air. Apt drying agents include methyl alcohol,ethyl alcohol, isopropyl alcohol, acetone and the like, suitably acetonebeing generally employed in the present process.

As hereinbefore described an alginate rope product according to thepresent invention is advantageous in terms of its structural integrityand there is provided by the present invention an alginate rope having adry tensile strength of at least 75 N/g. There is further provided bythe present invention an alginate rope having a wet tensile strength ofat least 25 N/g.

The terms `dry tensile strength` and `wet tensile strength` as usedherein denote the maximum load to breaking per gram of sample, theformer relating to a dry sample and the latter relating to a wet samplesuitably saturated by an appropriate solvent, such as ringers solutionand the like. Further details of the `dry tensile strength` and the `wettensile strength` are given in the accompanying Examples. All numbers inN/g herein obtained using a 10 cm gap between jaws on test rig.

Aptly an alginate rope according to the present invention has a drytensile strength of at least 150 N/g and more aptly at least 200 N/g. Interms of wet tensile strength an alginate rope according to the presentinvention suitably has a strength of at least 50 N/g, and more suitablyat least 100 N/g.

An alginate rope according to the present invention suitably has anabsorbency in the range of 1 to 10 g of ringers solution per g ofalginate rope, and more suitably an absorbency in the range of 2 to 6 gof ringers solution per g of alginate rope.

Alginates are produced by a variety of micro-organisms and marine algaewhich are the normal commercial source. The alginates being naturalmaterials show considerable variety but are characterised in being blockcopolymers, the individual monosaccheride units being arranged intogroups as blocks of mannuronic (M) and guluronic (G) residues. Inaddition to the repeating blocks each polymer chain can contain aproportion of alternating M and G monosaccharide units.

Suitably alginate fibres-employed in the absorbent layer may be high Mor high G, typically 60-80% by weight M or G respectively.

It is generally preferred however that when it is required to obtain analginate rope of relatively high tensile strength, such as 250 N/g to350 N/g dry tensile strength or 140 N/g to 150 N/g wet tensile strength,a high G alginate is employed. Such a high G alginate rope according tothe present invention is typically capable of absorbing 2 to 4 g ofringers solution per g of alginate rope. Alternatively if it is requiredto obtain a relatively more absorbent alginate rope according to thepresent invention, suitably having an absorbency of 4 to 6 g of ringerssolution per g of alginate rope, such a rope having relatively lower drytensile strengths and wet tensile strengths of 200 N/g to 250 N/g and125 N/g to 135 N/g respectively, it is generally preferred to employ ahigh M alginate.

An advantage associated with a process according to the presentinvention is that by varying the relative rotational speed of thespinneret, and linear extrusion speed achieved thereby, the strength andabsorptive properties of the resultant rope can be varied. For example,in the case where a relatively strong rope product is required, suitablyas described above with a dry tensile strength in the range of 250 N/gto 350 N/g or a wet tensile strength in the range of 140 N/g to 150 N/gand capable of absorbing 2 to 4 g of ringers solution per g of alginate,the fibres are extruded at a speed in the range of 4 to 10 meters/minute(preferably 5 meters/minutes) and the spinneret is rotated at a speed inthe range of 33 to 37 rpm (preferably 35 rpm). In an alternativeembodiment, wherein it is required to obtain a more absorptive rope asdescribed above, typically being capable of absorbing 4 to 6 of ringerssolution per g of alginate, and having a dry tensile strength of 200 N/gto 250 N/g or a wet tensile strength of 125 N/g to 135 N/g, the relativelinear and rotational speeds are suitably 4 to 10 meters/minute(preferably 5 meters/minute) and 28 to 32 rpm (preferably 30 rpm).

Typically an alginate rope having a dry tensile strength in the range of250 N/g to 350 N/g or a wet tensile strength in the range of 140 N/g to150 N/g prepared as above is particularly suitable for use as in thepreparation of yarns and woven fabrics, wherein structural integrity isdesirable in order to withstand the stresses imparted by conventionalknitting procedures. Furthermore, alginate rope products exhibiting theabove-mentioned strength are suitable for use as gingival retractioncords, wherein a highly twisted product may be desirable forfacilitating arrangement of the cord around the bed of a tooth; skilledworkers can appreciate that a loosely twisted product can bedisadvantageous in that an insertion implement, such as a spatula or thelike, could pass through gaps in the loosely twisted product therebymaking arrangement of the cord around the bed of the tooth problematic.On the other hand, the provision of a more absorptive rope as describedabove is particularly suitable for use in the treatment of highlyexuding wounds, sinus cavities and the like. In conjunction with theabove-mentioned absorptive properties, such ropes would exhibit atensile strength of a dry tensile strength of 200 N/g to 250 N/g or awet tensile strength of 125 N/g to 135 N/g, thereby facilitating removalthereof from a wound site or cavity.

There is further provided by the present invention an alginate ropeobtained by a process substantially as hereinbefore described.

An alginate rope according to the present invention is suitably of 1 to4 mm in thickness, 6 to 10 mm wide and is cut to a required lengthdepending on the desired application.

Both high M and high G ropes according to this invention offer theadvantages of excellent dimentional stability which make application ofa dressing consisting of or comprising the role particularly easy todeep or cavity wounds such as sinuses. In use high G containingdressings are particularly good in retaining their integrity even afterextended periods present in the deep or cavity wounds so that removal ofthe intact or largely intact dressing is greatly facilitated. This is aparticular advantage of such dressings of the invention since removal oftraditional dressings from deep or cavity wounds is a considerableproblem often requiring significant nursing time. In use high Mcontaining dressings can dissolve in wound exudate allowing for thedressings to be removed by washing out the wound with sterile salinesolution, water or the like.

The dressing of this invention may simply consist of the alginate ropepresented in suitable lengths, for example from 1 to 30 cms, moreusually 2 to 20 cms, for example 10 or 15 cm lengths. The dressing mostaptly is provided sealed in a bacteria proof pouch or pack, for exampleof foil, plastics or even an appropriate paper. Such pouches andpackages are well known to the skilled worker as are methods of sealingand sterilizing.

From one aspect this invention provides a ribbon-like dressing suitablefor dressing cavity wounds, which dressing comprises twisted alginatefibres whereby enhanced dimensional stability is produced. By enhanceddimensional stability it is meant that at least 4 times, more aptly atleast 8 times and preferably at least about 10 times as much force isrequired to pull the dressing apart (perpendicular to its length) thanin an analogous dressing wherein the alginate fibres are untwisted.

The present invention will now be further illustrated by the followingexamples which do not limit the scope of the invention in any way.

EXAMPLE 1

A 4 to 60% by weight sodium alginate solution in water was extruded intoa 12 liter spin bath containing a 0.2M aqueous solution of calciumchloride at 25° C. The alginate solution was extruded at a linear rateof 1.5 meter/minute through a spinneret (10000 holes, 75 microns)rotating at 10 rpm. The tow was drawn from the spinneret to give alinear draw ratio of 1.2. The fibres were stretched to 160 to 170% oftheir original length.

The product was then collected, washed in water, dried in acetone (20mls acetone per gram alginate; with a specific gravity of acetone in therange of 0.82-0.83) and air dried in an air stream at 25° C.

EXAMPLE 2

The tensile properties of a rope obtained by Example 1 and those of aknown alginate rope commercially available under the trade mark SORBSANwere investigated.

In order to determine the tensile strengths of an alginate ropeaccording to the present invention the following test conditions wereemployed:

Test Speed: 100.0 mm min⁻¹

Gauge Length: 100.0 mm

Load Cell: 500.0 N

Cell Class: 0.5%

Test conditions employed in the analysis of SORBSAN (trade mark) were asfollows:

Test Speed: 20.0 mm min⁻¹

Gauge Length: 100.0 mm

Load Cell: 20.0 N

Cell Class: 0.5%

The test speed and load cells employed in the analysis of SORBSAN (trademark) were lower than those for the alginate rope according to thepresent invention due to the lack of integrity observed for SORBSAN(trade mark). Similarly, both dry and wet tensile strengths wereinvestigated for the rope of the present invention whereas only the drytensile strength was investigated for SORBSAN (trade mark) due to theweakness of the product.

In order to investigate the wet tensile strength of the rope accordingto the present invention, the rope was soaked in ringers solution (142millimoles of sodium ions and 2.5 millimoles of calcium ions) for 1hour. After this time, the ringers solution was poured away and anyexcess liquid was allowed to drain prior to performing the test.

Tensile test results for the dry materials:

    ______________________________________                                                      Max Load Work Done (N-mm)                                       ______________________________________                                        High G alginate rope                                                                          63.57 (±12.60)                                                                        1557.0 (±737.0)                                   according to the                                                              present invention                                                             (2.07 g/m)                                                                    High M alginate rope 48.32 (±11.43) 1332.0 (±642.0)                     according to the                                                              present invention                                                             (2.07 g/m)                                                                    SORBSAN (trade mark) 0.22 (±0.14)  2.3 (±1.9)                           (2.18 g/m)                                                                  ______________________________________                                    

Tensile test results for samples according to the invention soaked inringers solution for 1 hour were as follows:

    ______________________________________                                                     Max Load Work Done (N-mm)                                        ______________________________________                                        High G alginate rope                                                                         29.84 (±4.03)                                                                         1212 (±186.0)                                      according to the                                                              present invention                                                             (2.07 g/m)                                                                    High M alginate rope 26.23 (±3.72) 1183 (±143.0)                        according to the                                                              present invention                                                             (2.07 g/m)                                                                  ______________________________________                                    

EXAMPLE 3

The absorbencies of a 60% M alginate rope and a 60% G alginate ropeaccording to the present invention were investigated.

The results are shown in Tables 1 and 2.

    __________________________________________________________________________    Sample: 60% M alginate rope (RINGERS SOLUTION - 30 MINUTES)                       Weight                                                                            Length               Weight g of                                         of of Length/ Weight Weight Weight fluid Weight of fluid                      intact intact unit of after of fluid absorbed/g absorbed by                   dressing dressing weight sample 30 mins absorbed of dressing intact                                            dressing                                    Sample (g) (cm) (cm/g) (g) (g) (g) (g/g) (g)                                  No. W.sub.1 L.sub.1 L.sub.2 W.sub.2 W.sub.3 W.sub.3 - W.sub.2 (W.sub.3                                          - W.sub.2)/W.sub.2 (W.sub.1 (W.sub.3                                          - W.sub.2))/W.sub.2                       __________________________________________________________________________    1   0.2149                                                                            9.5 44.2                                                                              0.2149                                                                            1.3772                                                                            1.1623                                                                             5.409  5.409                                       2 0.2093 9.5 45.4 0.2093 1.4152 1.2059 5.762 5.762                            3 0.2194 9.5 43.3 0.2194 1.3501 1.1307 5.154 5.154                            4 0.2134 9.5 44.5 0.2134 1.1850 0.9716 4.553 4.553                            5 0.2053 9.5 46.3 0.2053 1.1445 0.9392 4.575 4.575                            Mean 0.2125 9.5 44.7 0.2125 1.2944 1.0819 5.091 5.091                         S.D. 0.0054 0.0 1.2 0.0054 0.1214 0.1191 0.527 0.527                        __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Sample: 60% G alginate rope (RINGERS SOLUTION - 30 MINUTES)                       Weight                                                                            Length               Weight g of                                         of of Length/ Weight Weight Weight fluid Weight of fluid                      intact intact unit of after of fluid absorbed/g absorbed by                   dressing dressing weight sample 30 mins absorbed of dressing intact                                            dressing                                    Sample (g) (cm) (cm/g) (g) (g) (g) (g/g) (g)                                  No. W.sub.1 L.sub.1 L.sub.2 W.sub.2 W.sub.3 W.sub.3 - W.sub.2 (W.sub.3                                          - W.sub.2)/W.sub.2 (W.sub.1 (W.sub.3                                          - W.sub.2))/W.sub.2                       __________________________________________________________________________    1   0.2175                                                                            8.5 39.08                                                                             0.2175                                                                            0.8412                                                                            0.6237                                                                             2.868  0.6237                                      2 0.2253 8.5 37.73 0.2253 0.9724 0.7471 3.316 0.7471                          3 0.2142 8.5 39.68 0.2142 0.9731 0.7589 3.543 0.7589                          4 0.2129 8.5 39.92 0.2129 0.8180 0.6051 2.842 0.6051                          5 0.2081 8.5 40.85 0.2081 0.9942 0.7861 3.778 0.7861                          Mean 0.2156 8.5 39.45 0.5156 0.9198 0.7042 3.269 0.7042                       S.D. 0.0064 0.0 1.15 0.0064 0.0832 0.0834 0.412 0.0834                      __________________________________________________________________________

EXAMPLE 4

A 4 to 6% by weight sodium alginate solution in water at 20° C. wasextended into a 121 spin bath containing 0.2 m aqueous calcium chloridesolution at 20° C. The alginate was a high G alginate. The fibres wereextruded at a speed of 5 meter/minute through a spinneret (10,000 holes,75 microns) rotated at 35 rpm. The resulting two was treated asdescribed in Example 1 to provide a particularly strong rope.

EXAMPLE 5

Using the method of Example 3 but employing a high M alginate and arotational speed of 35 rpm, a particularly absorptive rope was obtained.

EXAMPLE 6

In order to compare the integrity and elasticity of the dressing ofExample 3 and an analogous rope produced without rotation, the materialswere tested perpendicular to the axis of spinning and testing involved,not breaking the sample, but extending the sample and returning thesample to the starting position.

All tensile tests were performed using the LLoyd LR5K material testingapparatus. The method involved using a set of clamps to hold thedressings (ropes) in place. Tests were performed by clampingapproximately 5 mm of the fibre perpendicular to the axis of spinning. Aseven fold extension was then applied to the fibre and following theextension the fibre was allowed to return to the starting position. Thiscycle was repeated five times. The results of these tests (mean andstandard deviation values) were as shown below.

Materials tested

i) G fibre of Example 3, 10,000 hole sample

ii) Analogous unrotated high G fibre, 10,000 hole sample

The test method for the ropes:

Test Speed: 20.0 mm min⁻¹

Gauge Length: 3.0 mm

Load Cell: 20.0 N

Cell Class: 0.5%

Tensile test results for the unrotated material:

    ______________________________________                                                MAX LOAD (N)      WORK DONE (N-mm)                                    ______________________________________                                        Sample 1                                                                             --                  --                                                    X 0.0238 X 0.1647                                                             S.D. 0.0008 S.D. 0.0129                                                      Sample 2 --  --                                                                X 0.0228 X 0.1430                                                             S.D. 0.0011 S.D. 0.0096                                                    ______________________________________                                    

Tensile test results for the rotated material of the invention:

    ______________________________________                                                MAX LOAD (N)      WORK DONE (N-mm)                                    ______________________________________                                        Sample 1                                                                             --                  --                                                    X 0.0249 X 1.703                                                              S.D. 0.0095 S.D. 0.158                                                       Sample 2 --  --                                                                X 0.2286 X 1.727                                                              S.D. 0.0094 S.D. 0.179                                                     ______________________________________                                    

The results show good reproducibility, both in terms of the max load andwork done for each sample. The most striking feature of the results,however, is the ten-fold increase in max load and work done for the ropeof this invention. This demonstrates that the method of the inventionadds great integrity of the sample.

We claim:
 1. A process for preparing an alginate rope, which process comprises the steps of:(a) extruding an aqueous solution of a water soluble alginate into a coagulation bath; (b) contacting the extruded water soluble alginate with a source of a cation capable of forming a water insoluble alginate salt so as to produce a tow of water insoluble alginate fibers; (c) twisting the water insoluble alginate fibers of the tow; and (d) stretching the fibers up to 250% of their original length.
 2. A process as claimed in claim 1 wherein the water soluble alginate is selected from the group consisting of sodium alginate, potassium alginate, lithium alginate, ammonium alginate and magnesium alginate.
 3. A process as claimed in claim 1 wherein the cation capable of forming a water insoluble alginate is selected from the group consisting of calcium and zinc.
 4. A process as claimed in claim 1 wherein the cation capable of forming a water insoluble alginate is in the form of a salt selected from the group consisting of chlorides, sulphates, nitrates, gluconnates and the like.
 5. A process as claimed in claim 1 wherein the process comprises an additional step of treating the water insoluble alginate fibers with a source of a cation capable of forming a water soluble alginate salt so as to replace at least some of the insolubilizing cations present in the alginate fibers with cations capable of forming a water soluble alginate salt.
 6. A process as claimed in claim 5 wherein the additional step is preceded by treatment of the fiber with an acid.
 7. A process as claimed in claim 5 wherein no more than about 20% of the insolubilizing cations are removed by the additional steps.
 8. A process for the preparation of an alginate rope as claimed in claim 15 wherein the rope comprises 30:70 Ca:Na to 90:10 Ca:Na mixed salt alginate fibers, and wherein the process comprises the additional steps of:(e) contacting the alginate fibers with an acid; and (f) treating the fibers with a source of a cation capable of forming a water soluble alginate salt so as to replace at least some of the insolubilizing cations present in the alginate fibers with cations capable of forming a water soluble alginate salt.
 9. A process as claimed in claim 8 wherein steps (e) and (f) are conducted in an acid bath whose contents include a suitable acid and a solubilizing cation.
 10. A process as claimed in claim 9 wherein the pH of the acid bath is in the range of 1 to
 3. 11. A process as claimed in claim 10 wherein the pH of the acid bath is in the range of about 1.5 to about 2.5.
 12. An alginate rope obtained by the process as claimed in claim
 1. 13. A method of treating cavity wounds comprising dressing the wound with an alginate rope obtained by the process as claimed in claim
 1. 